This invention relates generally to methods and devices for removing toxic materials, such as oxyanions of heavy metals and their radioactive isotopes, from aqueous streams and is particularly concerned with methods for removing such toxic materials from groundwater, waste-water and drinking water using rare earth compounds.
Toxic metals and their radioactive isotopes quite frequently find their way into the groundwater from geochemical reactions, industrial waste discharges, including those generated by nuclear power plants, past agricultural uses of pesticides containing toxic metals and other sources. Combinations of radioactive materials and toxic metals are often found in run-off waters near mining areas. Environmental regulations often require the removal of these toxic materials to extremely low levels.
Various technologies have been used in the past to remove metals from aqueous systems. Examples of such techniques include adsorption on high surface area materials, such as alumina and activated carbon, ion exchange with anion exchange resins, co-precipitation utilizing flocculants, and electrodialysis. However, most technologies for metals removal are not generally effective for removing a plurality of these metals and/or their radioactive isotopes. Moreover, techniques that have been used in large municipal water supplies to remove heavy metals to produce drinking water are not generally practical for residential applications because of space requirements and the need to use dangerous chemicals.
Thus, there is a need for new techniques to economically and effectively remove many different types of toxic metals from vast volumes of drinking water, well water and industrial waters. In addition, there is a need for these techniques to be capable of removing a variety of radioactive materials from these aqueous streams either alone or in combination with toxic non-radioactive metals.